Biomedical Engineering – From Theory to Applications

Column Coupling Electrophoresis in Biomedical Analysis
derivatization reaction for carnitine as the model analyte was carried out on a FI system
coupled with the CE equipment via a programmable arm (Valcárcel et al., 1998). The
arrangement is shown in Fig. 7. The derivatization reagent (FMOC-Cl) is introduced directly
into the loop of the injection valve (IV) when load position is selected, while the sample is
introduced into the system and it is mixed with the buffer (carbonate). Then, valve is
switched to the injection position allowing the mixing of sample–buffer and reagent
solution. In this position the flow is stopped for a defined time in the reactor loop (390 cm),
which is introduced into the thermostatic bath (50°C). Finally, the reaction mixture is
introduced via the mechanic arm into the CE system.
The third generation of flow-injection (laboratory-on valve, lab-on-valve or LOV) allows
scaling-down sample and reagent volumes to the 10–20 L range, while waste production is
typically 0.1–0.2 mL per assay (Solich et al., 2004). These facts make LOV an ideal tool for
on-line coupling with CE systems (Kulka et al., 2006).
3.1.2.2 SPE-CE
The new trends in the coupling between SPE–CE are focused on several strategies, one of
which involves developing new materials to increase the retention and selectivity of some
analytes. In this sense the increasing use of materials such as immunoaffinity sorbents has
been shown to overcome the problem of selectivity especially when complex samples are
analysed. The use of molecular imprinted polymers (MIP) could be also an attractive
alternative and further development is expected in this area in the near future. Carbon
nanostructures also seem to be very promising materials which are in the first stages of
development and so more research is expected in this field (Puig et al., 2007).
Fig. 8. Schematic diagram of the three types of interfaces for on-line SPE–CE coupling: (a)
vial interface; (b) valve interface; (c) T-split interface. Reproduced with permission from (a)
Stroink et al. (Stroink et al., 2003), (b) Tempels et al. (Tempels et al, 2007) and (c) Puig et al.
(Puig et al., 2007).
Extraction techniques now play a major role for sample preparation in CE. These techniques
can be used not only for reconstitution of the sample from small volumes but also for
sample purification in complex matrices and desalting for very saline samples that would
interfere with the electrophoretic process (e.g. FESS requires low conductivity sample).
Considerable progress has been made towards the coupling of solid phase extraction (SPE)
with a subsequent electrophoresis while coupling of liquid phase extraction (LLE) with
electrophoresis is less used. Before coupling the SPE and CE, the appropriate SPE conditions
for trapping and eluting the test compounds must be investigated. The breakthrough
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